As applications for ITS, for example, the following collision prevention system has been developed: when inter-vehicular (vehicle-to-vehicle) communication is performed, the position, speed, and the like of an own vehicle is transmitted, and the position, speed, and the like of any other vehicle is received to thus confirm a mutual positional relationship therebetween; when this positional relationship indicates the possibility of a collision between the mutual vehicles, the drivers are alerted.
In addition, the following signal oversight prevention system has been developed: when road-to-vehicle communication is performed, and when it is determined on the basis of the signal information received from a roadside communication system that the own vehicle, is not properly decelerated at a red light, the driver is alerted.
On the other hand, for example, in Patent Document 1, there is disclosed a wireless device that controls transmission of a packet signal storing therein information related to the driving state of an own vehicle depending on whether the vehicle is running or stopped. In the wireless device, if the on vehicle is running, the transmission of the foregoing packet signal is continued, and if the own vehicle is parked, the transmission of the foregoing packet signal is stopped assuming that safety support for the running vehicle is unnecessary. By doing so, the probability of a collision of the foregoing packet signal used for a safety support system is reduced.